Electronic phonograph pick-up



y 11, 1939- .J. c. SAMPSON,

ELECTRONIC PHONOGRAPH 'PICK-UP Filed Aug. 27, 1936 INVENTOR JOHN C. SAMPSON %7(% q I ATTORNEY Patented July 11, 1939 UNITED STATES ELECTRONIC PHONOGRAPH Pica-UP John C. Sampson, St. Louis, Mo., assignor of onehalf to Julian E. Sampson Application August 27, 1936, Serial No. 98,198

2 Claims.

10 it has been difllcult to make the diaphragm vibrate in exact accordance with the variations in the sound track'so that the variations in the electric current through the pick-up have been entirely responsive to the recorded sound. One of 14 the chief dimculties has been in producing a stylus and diaphragm capable ofeliminating the scratching caused by the stylus tracking over the sound track. According to my invention I connect the stylus with an element of a thermionic 20 tube in such a manner as to cause variation of the current flowing through the tube in accordance with the variations in the sound track.

It is an object of the invention to provide an electric pick-up for a phonograph which will pro- 25' duce variations in current exactly corresponding to the variations in the sound track.

It is a further object of the invention to produce an electric pick-up capable of completely eliminating the scratching sound without, in any 30 way, aflecting the volume of the recorded sound.

Other objects of the invention will appear from the following description and accompanying drawing, referring to which the figure is a diagram indicating the approximate mechanical 35 construction and electrical connections of a device built in accordance with my invention.

The reference numeral I indicates the base of a thermionic tube having a vacuum chamber 2,

preferably formed of metal. The end of the tube,

40 opposite the base, is closed witha slightly flexible diaphragm 3 which is preferably made of thin steel or other suitable material. The vibration of the diaphragm is preferably damped by a coat ing of lead or rubber to avoid setting up a har- 45 monic vibration due to its own inertia. The grid 4 is attached to the center of the diaphragm and extends through the diaphragm for attachment to a stylus retaining member 5 in which the conventional stylus or phonograph needle 6 is fixed 50 by any suitable means, such as the set screw 1.

The thermionic tube is provided with a conventional cathode 8 which is heated by the filament 9. A plate I ll is also mounted in the vacuum chamber opposite the cathode. Suitable ter- 66 minals are provided at the base of the tube, the

terminal H being connected to the cathode, l2 and i3 to the filament, [4 to the plate and I5 to the ground. It will be understood that the grid 4 is grounded by reason of its connection to the steel diaphragm 3, themetallic-vacuum chamber 5 2, and the base I which is grounded at IS,

A source of current which is indicated by the reference numerals B plus and B minus is provided for maintaining suitable charges on the cathodes and plate, This current may be derived 10 from any desired source but preferably originates in the 1l0-volt A. C. line which is available everywhere. The plus'terminal of the source B is connected through the plate resistance l6 to the terminal l4. A suitable condenser l1, having one grounded terminal, is also connected to the plus terminal of the source. The plate terminal i4 is connected to one terminal of the condenser 18, the other terminal of which is connected to the in-put grid of an amplifier I9.

The cathode terminal H is connected to a variable resistance 20, one terminal of which is grounded so as to form a connection with the grounded negative terminal of the source of current supplied B minus. A suitable condenser 2|, one terminal of which is grounded, is also connected to the cathode terminal H. Any desired source of current 22 may be used for heating the filament 9. It will be understood that many of the elements described herein are very well known 0 and that they may be widely varied without departing from the scope of my invention which relates chiefly to the mechanical movement of any one or more of the electrical elements in the thermionic tube by means of a stylus or sound track, or other mechanical means.

In operation the cathode 8, being coated with a suitable radioactive material and heated by the filament 9 emits electrons or negative particles of electricity, which form a cloud around the cathode and tend't-o flow through thevacuum to the positively charged plate N. The grid 4 is grounded as previously described and the effect of the variable resistance 20 connected in the lead to the cathode 8 gives the cathode a positive charge with respect to the grid. This is the same thing as saying that the grid 4 will become more negative with respect to the cathode 8 as the value of the variable resistance 20 increases. We

can, therefore, control the volume of output through the cathode-grid circuit by varying the condition of the variable resistance 20.

The eiiect of the grid 4 is to resist the flow of electrons from the cathode 8 to the plate I0. Movement of the grid toward the cathode will increase the flow of electrons while movement in the opposite direction will permit the flow to decrease. This movement is produced by running the stylus 6 in the sound track of a phonograph record or similar device as indicated at 23. It

will be understood that this movement gives the -v stylus 6 a movement to the right orvleft with respect to Figure 1 turning the unitary stylus and grid about the center 01 the diaphragm 3, as a pivot so that the grid is moved toward and away from the cathode in accordance with the variations of the sound track. This, in turn, produces variations in the flow of current from the cathode to the plate and corresponding variations in the charge of the condenser l8 which are communicated through its connection to the amplifier l9. It will be noted that the up and down variations due to scraping of the needle on the bottom of the groove merely causing up and down movement of the grid which has no substantial efiect on transmission of current from the cathode to the plate so that the well known scratching sound is substantially eliminated. It will also be understood that the use of the invention is not limited to a sound track with sideways variations because the use of the device can be adopted to up and down sound tracks by merely bending the stylus to the proper position.

It will be understood that variations in the construction of the above described device may be made by those skilled in the art and, accordingly, I do not wish to be limited in my protection except as indicated in the following claims.

I claim:

1. A thermionic tube having avacuum chamber, grid, plate and cathode elements for said chamber, a part of the wall of said chamber being at least slightly flexible, one of said elements being connected to the flexible part of said wall and mechanical means for flexing said wall, and a layer of non-resilient solid material engaging said flexible wall part to damp vibration thereof.

2. A thermionic tube having a vacuum chamber, grid, plate and cathode elements for said chamber, a part of the wall of said chamber being at least slightly flexible, one of said elements being connected to the flexible part of said wall, and mechanical means for flexing said wall,' that part of the flexible wall to which said element is attached being coated with a metal having great density and little elasticity.

JOHN C. SAMPSON. 

